Despite the maturity of existing temperature-swing carbon capture technologies, they are too expensive to be implemented at the scale recommended by the IPCC for achieving international climate goals. This cost is dictated by the process thermodynamics and kinetics, which respectively determine the bulk of ongoing costs via energy consumption and capital costs via absorber sizing. Other researchers identified multiple electrochemical carbon capture approaches with promising laboratory scale energy consumption, albeit often at slow capture rates. We developed computational models of the most widely-studied absorption-based aqueous electrochemical approaches (e.g. pH swings by proton-coupled electron transfers and reversible sorbent inhibition by metal electrowinning) to determine the fundamental limits of the energy demands and CO2 fluxes, as well as their potential trade-offs. These models simulated idealized scenarios with perfect efficiencies, ruling out operating conditions that would never outperform the industry-standard amine scrubbing process due to, for instance, the sorbent concentration. We generalized our simulations using realistic but randomized chemical properties (e.g. pKas and rate constants) rather than constraining property values to known compounds, accounting for the fact that many potential compounds lack literature data. To make the problem tractable, we trained Gaussian processes on adaptively sampled simulations to provide sufficiently accurate energy and flux estimates while minimizing computationally expensive simulation runs. We identified that electrochemical processes have an optimal set of reaction equilibria that balances favorable CO2 removal and facile sorbent regeneration. For example, capture by PCET-driven pH swings achieved both low energies and fast kinetics when the pKas of the reduced species were similar to those of bicarbonate and carbonic acid. We found that electrochemical carbon capture has more favorable fundamental limits than amine-scrubbing with respect to both energy demand and capture rates, and our simulations provide insight into which chemical properties are most important when selecting compounds to achieve these goals.

Determining the fundamental limits of aqueous absorption-based electrochemical carbon capture

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.